This invention relates generally to downhole tools for use in oil and gas wellbores, and more particularly, to such tools having drillable components made from metallic or non-metallic materials, such as soft steel, cast iron, engineering grade plastics, and composite materials and further having buttons incorporated into anti-slip elements which facilitate the setting and anchoring of downhole tools such as drillable packer and bridge plug tools in wellbores.
In the drilling or reworking of oil wells, a great variety of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of the well, such as when it is desired to pump cement or other slurry down the tubing and force the slurry out into a formation. It thus becomes necessary to seal the tubing with respect to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well. Downhole tools referred to as packers and bridge plugs are designed for these general purposes and are well known in the art of producing oil and gas.
The EZ Drill.RTM. SV.RTM. Squeeze Packer, for example, includes a set ring housing, upper slip wedge, lower slip wedge, and lower slip support made of soft cast iron. These components are mounted on a mandrel made of medium hardness cast iron. The EZ Drill.RTM. Squeeze Packer is similarly constructed. The Halliburton EZ Drill.RTM. Bridge Plug is also similar, except that it does not provide for fluid flow therethrough.
All of the above-mentioned packers are disclosed in Halliburton Services--Sales and Service Catalog No. 43, pages 2561-2562, and the bridge plug is disclosed in the same catalog on pages 2556-2557.
The EZ Drill.RTM. Packer and the EZ Drill.RTM. Bridge Plug and the EZ Drill.RTM. SV.RTM. Packer are designed for fast removal from the well bore by either rotary, cable tool, or coiled tubing drilling methods. Many of the components in these drillable packing devices are locked together to prevent their spinning while being drilled, and the harder slips are grooved so that they will be broken up in small pieces. Typically, standard "tri-cone" rotary drill bits are used which are rotated at speeds of about 75 to about 120 rpm. A load of about 5,000 to about 7,000 pounds of weight is applied to the bit for initial drilling and increased as necessary to drill out the remainder of the packer or bridge plug, depending upon its size. Drill collars may be used as required for weight and bit stabilization.
Such drillable devices have worked well and provide improved operating performance at relatively high temperatures and pressures. The packers and bridge plugs mentioned above are designed to withstand pressures of about 10,000 psi (700 Kg/cm.sup.2) and temperatures of about 425.degree. F. (220.degree. C.) after being set in the well bore. Such pressures and temperatures require using the cast iron components previously discussed.
In order to overcome the above long standing problems, the assignee of the present invention introduced to the industry a line of drillable packers and bridge plugs currently marketed by the assignee under the trademark FAS DRILL.RTM.. The FAS DRILL.RTM. line of tools consist of a majority of the components being made of non-metallic engineering grade plastics to greatly improve the drillability of such downhole tools. The FAS DRILL.RTM. line of tools have been very successful and a number of U.S. patents have been issued to the assignee of the present invention, including U.S. Pat. No. 5,271,468 to Streich et al., U.S. Pat. No. 5,224,540 to Streich et al., U.S. Pat. No. 5,390,737 to Jacobi et al., U.S. Pat. No. 5,540,279 to Branch et al., U.S. Pat. No. 5,701,959, Hushbeck et al., and pending U.S. patent application Ser. No. 08/888,719 filed Jul. 7, 1997, to Yuan et al.
The preceding patents are specifically incorporated herein.
The tools described in the above references typically make use of metallic or non-metallic slip-elements, or slips, that are initially retained in close proximity to the mandrel but are forced outwardly away from the mandrel of the tool upon the tool being set to engage a casing previously installed within an open wellbore. Upon the tool being positioned at the desired depth, or position, the slips are forced outwardly against the inside of the casing to secure the packer, or bridge plug as the case may be, so that the tool will not move relative to the casing when for example operations are being conducted for tests, to stimulate production of the well, or to plug all or a portion of the well.
It is known within the art that cylindrically shaped inserts, or buttons, may be placed in such slip elements, especially when such slip elements are made of a non-metallic material such as plastic composite material, to enhance the ability of the slip elements to engage the well casing. The buttons must be of sufficient hardness to be able to partially penetrate, or bite into, the surface of the well casing which is typically steel. However, especially in the case of downhole tools being constructed of materials that lend themselves to being easily drilled from the wellbore once a given operation involving the tool has been performed, the buttons must not be so hard or so tough to resist drilling or fouling of the cutting surfaces of the drilling bit or milling bit.
Currently, it is known that buttons made of zirconia ceramic materials offer to a certain extent, the desirable characteristics of being of a sufficient hardness to bite in the casing upon setting the tool, but are not so tough as not to be drillable when it comes time to remove the tool from the wellbore. However, it has become evident that the first portion of the button to contact the casing which is usually the most protruding or leading edge of the cylindrically shaped buttons made of such zirconia ceramic materials are brittle and therefore prone, if not expected, to chip or fracture as the slip element engages with the well casing. Many times, such chipping along the leading edge does not degrade the anti-slipping ability of the tool to a level that the tool actually slips in the casing under normal conditions. However, under extremely high pressures or temperatures the undesired chipping could adversely affect the anti-slip performance of the slip elements because the button would not be able to bite as deeply into the casing as would be possible if the leading edge were not chipped during the setting of the tool.
In order to remedy the problematic chipping characteristic associated with zirconia ceramic buttons, tungsten-carbide material from Retco Tool Co. has been used to form buttons. The tungsten carbide buttons offer enhanced anti-chipping characteristics but do so at the expense of not being as easy to drill or mill as the zirconia buttons when destructively removing the tool from the cased wellbore due to the extreme hardness, higher density, and toughness of the tungsten carbide buttons. Such drilling and milling problems include the tungsten carbide buttons fouling, dulling, difficulty in circulating pieces of the buttons within fluids that may be present in the well bore, and the tungsten carbide buttons simply resisting the cutting edges of the drilling or milling tools. Such resistance causes increased costs associated with the rig and tool crews having to expend more time to manipulate the drill string in order to successfully drill, or mill, the tool from the wellbore.
Thus, there remains a need in the art to identify slip button materials that are sufficiently hard to resist chipping upon biting into the wellbore casing yet not be so tough as to unduly resist drilling or milling when it comes time for the tool having such buttons to be destructively removed from the wellbore casing.
There also remains a standing need in the art to identify cost effective technically suitable slip button materials that are able to withstand the various chemicals, temperatures, mechanical loadings, and pressures encountered in downhole environments.